A Stereological Analysis of the Numerical Distribution of Neurons in Dorsal Root Ganglia C4-T2in Adult Macaque Monkeys

Abstract

The numbers of neurons in dorsal root ganglia C₄-T₂ of adult macaque monkeys (M. nemestrina) were estimated in celloidin-embedded material by means of the optical fractionator, a stereological procedure that combines the optical disector with a fractionator sampling scheme. On each side, counts of A-type, B-type, and total neurons were performed for the whole set of ganglia, as well as separately for ganglia C₇, C₈, and T₁. Sampling and counting in this study were carried out with the help of an interactive computer system, the test grids being provided by the GRID® general stereological software package (Olympus Denmark). The precision of the estimates for each animal was evaluated by computing the coefficient of error, which was kept at or below 0.10. The mean number of neurons on each side of the C₄-T₂ set was 236,500, with a coefficient of variation among animals (CV) of 0.13. Of these neurons, 42% were A-type and 56% were B-type. Mean left-right differences among animals were below 1%, with low variability (CV = 0.07). The mean numbers of neurons in ganglia C₇, C₈, and T₁ were, respectively, 46,000 (CV = 0.20), 51,000 (CV = 0.18), and 41,000 (CV = 0.22). Mean side differences for individual ganglia were 17%, 16%, and 12%, respectively, with high variability among animals. Intraanimal side differences were low for the whole set of ganglia (4%), as well as for the C₇-T₁ group (5%), but increased substantially when ganglia were considered separately (up to 17% on average in C₇) or even in pairs of adjacent ganglia. These findings provide a quantitative frame for developmental or lesion studies in the peripheral somatosensory system of macaques, and warn against using single ganglia in studies requiring quantitative side comparisons.